Method for venting a cylinder of a piston-cylinder unit of a power brake pressure generator of a hydraulic power brake system

Abstract

Venting a cylinder of a piston-cylinder unit of a power brake pressure generator of a hydraulic power brake system for a motor vehicle. A piston in the cylinder is displaced from a forward-displaced position back into a home position and subsequently forward again. When the piston is displaced back, a connection valve is closed so that the piston sucks brake fluid from a brake fluid container, the brake fluid flowing over a lip seal acting in the manner of a pressure relief valve as the first piston seal. During the forward stroke, the piston pushes brake fluid through the then open connection valve into the brake fluid container. Any air contained in the cylinder is pushed with the brake fluid from the cylinder and separates from the brake fluid in the brake fluid container.

The invention claimed is: 
     
       1. A method for venting a cylinder of a piston-cylinder unit of a power brake pressure generator of a hydraulic power brake system, wherein the cylinder of the piston-cylinder unit of the power brake pressure generator is connected by a plunger valve to a brake circuit of the power brake system and by a connection valve to a brake fluid container, and wherein a piston of the piston-cylinder unit in the cylinder of the piston-cylinder unit is sealed with a first piston seal, which can be overflowed from the brake fluid container into the cylinder of the piston cylinder unit of the power brake pressure generator in the manner of a pressure relief valve in the event of a negative pressure in the cylinder of the piston-cylinder unit of the power brake pressure generator relative to a pressure in the brake fluid container, the method comprising the following steps:
 displacing, with the plunger valve closed and the connection valve closed, the piston of the piston-cylinder unit of the power brake pressure generator from a forward-displaced position back in a direction of a home position, wherein the piston generates a negative pressure in the cylinder of the piston-cylinder unit of the power brake pressure generator in such a way that brake fluid is sucked from the brake fluid container, flows over the first piston seal and flows into the cylinder of the piston-cylinder unit of the power brake pressure generator; and 
 subsequently displacing again, with the connection valve open and the plunger valve closed, the piston forward in a direction of a displacement stroke in the cylinder of the piston-cylinder unit of the power brake pressure generator, so that brake fluid is pushed from the cylinder of the piston-cylinder unit of the power brake pressure generator through the open connection valve into the brake fluid container. 
 
     
     
       2. The method according to  claim 1 , wherein the method is repeated. 
     
     
       3. The method according to  claim 1 , wherein, when the piston of the piston-cylinder unit of the power brake pressure generator is in the home position, the plunger is displaced into the forward-displaced position with the connection valve open and the plunger valve closed, before it is displaced back in the direction of the home position in the cylinder of the plunger cylinder unit of the power brake pressure generator with the plunger valve closed and the connection valve closed. 
     
     
       4. The method according to  claim 1 , wherein, with the plunger valve closed and the connection valve closed, the piston of the piston-cylinder unit of the power brake pressure generator is displaced in the direction of the displacement stroke, a hydraulic pressure in the cylinder of the piston-cylinder unit of the power brake pressure generator is measured and the steps are performed or repeated when the pressure is too low. 
     
     
       5. The method according to  claim 1 , wherein the first piston seal includes a lip seal, a sealing lip of which acts in the manner of a pressure relief valve and which can be overflowed from the brake fluid container into the cylinder in the event of a negative pressure in the cylinder of the piston-cylinder unit of the power brake pressure generator relative to a pressure in the brake fluid container and which can seal against a flow from the cylinder into the brake fluid container between the piston and the cylinder of the piston-cylinder unit of the power brake pressure generator. 
     
     
       6. The method according to  claim 1 , wherein the cylinder of the piston-cylinder unit of the power brake pressure generator is connected to the brake fluid container via the first piston seal through a different brake line than via the connection valve. 
     
     
       7. The method according to  claim 1 , wherein the cylinder of the piston-cylinder unit of the power brake pressure generator has a groove, which extends in an axial direction of the cylinder at an inner circumference of a chamber of the cylinder delimited by the piston in the cylinder and through which brake fluid can flow between the piston and the cylinder and which ends at a small distance from the first piston seal. 
     
     
       8. The method according to  claim 1 , wherein a brake line connecting the connection valve to the cylinder of the piston-cylinder unit of the power brake pressure generator opens into the cylinder at a top in a usage position of the piston-cylinder unit.